1. Field of the Invention
The present invention relates to a rotation angle detecting device for detecting the number of rotations in various machines and equipments, for example, for detecting the number of rotations for the purpose of controlling a compact motor or for detecting the number of rotations for the purpose of detecting of a position of a business machine or equipment, and also to a bearing assembly equipped with such rotation angle detecting device.
2. Description of the Prior Art
A rotation angle detecting device that can be incorporated in a small size machine and is capable of detecting the rotation angle with high precision has been suggested, in which a magnetic sensor array is employed. (See, for example, the Japanese Laid-open Patent Publication No. 2004-37133, published Feb. 5, 2004). This is of a type, in which magnetic sensor arrays each including a plurality of magnetic sensor elements (MAGFET) is integrated on a sensor chip together with signal amplifying circuits, analog-to-digital (AD) converter circuits and a digital signal processing circuit and such sensor chip is disposed in face-to-face relation with a magnet arranged on a rotatable member. In such case, the magnet is of a kind having an anisotropy in a circumferential direction about the axis of rotation and, on the sensor chip referred to above, four magnetic sensor arrays 35A to 35D are arranged in a generally rectangular pattern, each array extending along one of the four sides of the rectangular shape, as shown in FIG. 13. The digital signal processing circuit 33 is disposed inside the rectangular arrangement of the magnetic sensor arrays 35A to 35D.
With the rotation angle detecting device so structured and so configured as hereinabove described, the magnetic sensor arrays 35A to 35D are utilized to detect a magnetic field applied in a direction perpendicular to the sensor chip and respective outputs from those magnetic sensor arrays 35A to 35D are read out by the digital signal processing circuit 33 through the associated signal amplifier circuits 31 and the associated AD converting circuits 32, so that the digital signal processing circuit 33 can detect a zero-crossing-position, which corresponds to an NS boundary of the detected magnetic field on each of the sensor arrays 35A to 35D, to thereby calculate the angle of rotation of the magnet.
In the rotation angle detecting device of the structure described above, pixels forming each of the magnetic sensor arrays 35A to 35D are made up of a plurality of magnetic sensor elements connected parallel to each other so that effects which may be brought about by sensor noises and offset errors, can be reduced by averaging. Although increase of the number of the magnetic sensor elements that are to be connected parallel to each other may result in reduction of the noise, the area occupied by each pixel increases. On the other hand, in terms of highlighting the detecting capability, it is desirable not to increase the pitch of arrangement between each neighboring pixels so much, and, therefore, the magnetic sensor elements that are connected parallel to each other are arranged in a direction widthwise of the magnetic sensor arrays 35A to 35D. As a result, the magnetic sensor arrays 35A to 35D tend to have an increased line width.
In this case, in the circuit configuration in which each of the signal amplifying circuits 31 and each of the AD converting circuits 32 are disposed between the digital signal processing circuit 33 and the respective magnetic sensor array 35A to 35D as shown in FIG. 13, an increase of the width of each of the magnetic sensor arrays 35A to 35D makes it difficult to secure a sufficient space for installation of the associated signal amplifying circuits 31 and the associated AD converting circuits 32.
Also, the digital signal processing circuit 33 has a digital circuit configuration and tends to break out considerable digital noises and, therefore, the signal amplifying circuits 31 and the AD converting circuits 32, both located peripheral to the digital signal processing circuit 33 and having an analog circuit configuration, tend to be adversely affected, constituting a cause of deterioration of the detecting accuracy with which the angle can be detected.